It depends on what you are looking for.
Boma is a buffet. It's huge, noisy, and there are tons of choices here. If you are not adventurous, you may not like a lot of the selections, particularly in the soup and vegetable pods. I love the decor here and I love the various pods. The childrens' pod and the dessert pod both offer a great selection.
Jiko is more upscale, quiet, outstanding wine selection. The restaurant is dark and soothing with a slower paced service. For me, the best part of the meals here are always the appetizers, particularly the soups. The entrees and desserts are ok but not at the same level. I would not eat here if I wasn't having appetizers.